Every creature needs to rest. Giraffes, little babies, elephants, dogs, cats, kids, koala bears, grandparents, moms, dads, and hippos in the jungle — they all sleep! Just like eating, sleep is necessary for survival.
Sleep gives your body a rest and allows it to prepare for the next day. It's like giving your body a mini-vacation. Sleep also gives your brain a chance to sort things out. Scientists aren't exactly sure what kinds of organizing your brain does while you sleep, but they think that sleep might be the time when the brain sorts and stores information, replaces chemicals, and solves problems.
The amount of sleep a person needs depends a lot on his or her age. Babies sleep a lot — about 14 to 15 hours a day! But many older people only need about 7 or 8 hours of sleep each night. Most kids between the ages of 5 and 12 years old are somewhere in between, needing 10 to 11 hours of sleep. Some kids might need more and some need less. It depends on the kid.
Skipping 1 night's sleep makes a person cranky and clumsy. After missing 2 nights of sleep, a person will have problems thinking and doing things; his or her brain and body can't do their normal tasks nearly as well. After 5 nights without sleep, a person will hallucinate (this means seeing things that aren't actually there). Eventually, it becomes impossible for the brain to give its directions to the rest of the body without sleep — the brain needs to spend time in bed and catch its ZZZs!